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Black children in the United States are more likely to experience childhood adversity than white children, and these disparities are reflected in changes to regions of the brain linked to psychiatric disease like posttraumatic stress disorder (PTSD), according to new research reported by Harvard Medical School researchers at McLean Hospital.
The findings, published in the February issue of the American Journal of Psychiatry, suggest that adversity may act as a toxic stressor to regions of the brain related to threat processing and that this exposure is disproportionately seen in Black children.
The authors added that their study provides additional evidence contradicting the pseudoscientific falsehood that there are inherent race-related differences found in the brain and instead emphasizes the role of adversity brought on by structural racism.
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For the study, Nathaniel Harnett, HMS assistant professor in psychiatry and director of the Neurobiology of Affective Traumatic Experiences Laboratory at McLean Hospital, led a team of researchers in their analysis of surveys and MRI brain scans of more than 7,300 white children and nearly 1,800 Black children in the U.S. who were between 9 and 10 years old.
They found that Black children displayed small neurobiological differences reflected as lower gray matter volumes in the amygdala, hippocampus, and prefrontal cortex compared with white children.
Their analysis also revealed that experiencing adversity was the significant differentiating factor, with household income the most common predictor of brain volume differences.
“Our research provides substantial evidence of the effects structural racism can have on a child’s developing brain. These small differences may be meaningful for their mental health and well-being through adulthood.
“The dataset in our study included children younger than 10 years old — children who have no choice in where they are born, who their parents are, and how much adversity they are exposed to. These findings offer another chilling reminder of the public health impact of structural racism and how crucial it is to address these disparities in a meaningful way,” said Harnett.
In the U.S., there are stark racial disparities in the distribution of economic resources, exposure to stress, and psychiatric disorder prevalence. To date, there have been few studies investigating how racial inequities in the social determinants of health may lead to changes in the brain for different groups.
Mining datasets to uncover disparities, neurological effects
For their study, Harnett and colleagues at McLean’s Neurobiology of Fear Laboratory, founded and directed by Kerry Ressler, HMS professor of psychiatry and chief scientific officer at McLean, and a researcher on the study, leveraged strong datasets to look for potential race-related differences in the neurobiology of psychiatric disorders and how racial structural inequities might explain the differences.
The researchers reviewed data from the 2019 Adolescent Brain and Cognitive Development Study, a large-scale research effort that included nearly 12,000 U.S. children between the ages of 9 and 10 from 21 sites across the country.
Study participants’ parents completed surveys assessing parent and child race and ethnicity, parental education, employment and family income, and other variables. Participating children completed assessments that captured emotional and physical conflicts within their households.
Also included were measures of neighborhood disadvantage using the Area Deprivation Index, which uses 17 socioeconomic indicators from the U.S. Census Survey, including poverty and housing, to characterize a given neighborhood.
The analysis found that white children’s parents were three times more likely to be employed than Black children’s parents.
White children’s parents also attained a higher level of education and had greater family income compared with Black children’s parents. Specifically, about 75 percent of white parents had a college degree compared with nearly 41 percent of Black parents, and about 88 percent of white parents earned $35,000 a year or more compared with about 47 percent of Black parents.
White children also reported experiencing less family conflict, less material hardship, less neighborhood disadvantage, and fewer traumatic events than Black children did.
When assessing corresponding MRI data, experiencing childhood adversity was associated with lower gray matter volumes in the amygdala, hippocampus, and prefrontal cortex, and these effects were more likely to be seen in Black children.
The amygdala plays an important role in the learning of a fear response, the hippocampus is key to memory formation, and the prefrontal cortex regulates the emotional and threat response to fear.
The researchers observed neurobiological effects tied to most adversity indicators, with income being the most frequent predictor, affecting gray-matter volume in eight of 14 regions of the brain studied.
Trauma history and family conflict were not related to gray-matter volume in any of the models; however, the researchers note that this finding doesn’t necessarily indicate no neurobiological effect from those adversities.
“The overall differences in the brain were small and partially accounted for by the differences seen in socioeconomic status, which is important,” said Harnett. “The disparities in lived adversity is what drove these differences.”
Additional analysis factoring in previous studies on PTSD and regions of the brain in Black children had significantly greater PTSD symptom severity, and symptom severity was further predicted by adversity.
Future direction of the research
In an effort to track the neurobiological effects that racial disparities in adversity have throughout a lifetime, the team plans to build upon these findings and expand their data collection beyond the ages included in this study. The researchers also hope to determine whether exposure to adversity may accelerate or decelerate aging in the brain and whether additional measures of adversity not included in this study may impact these brain regions or others involved in psychiatric disorders.
“These findings may just be the tip of the iceberg,” said Harnett.
Authorship, funding, disclosures
Additional authors include Nathalie Dumornay, Division of Depression and Anxiety Disorders, McLean, and Lauren Lebois, HMS Department of Psychiatry and the Division of Depression and Anxiety Disorders, McLean.
Support for this research was provided by the National Institute of Mental Health (K00MH119603, K01MH118467, and U01MH110925).
Lebois has served as an unpaid member of the Scientific Committee for the International Society for the Study of Trauma and Dissociation, and her spouse receives payments from Vanderbilt University for technology licensed to Acadia Pharmaceuticals. Ressler has served on advisory boards or as a consultant for Acer, Bionomics, BioXcel, the Brain Research Foundation, Janssen, Jazz Pharmaceuticals, Sage, Takeda, and Verily, and he has received sponsored research support from Alkermes, Alto Neuroscience, BrainsWay, Genomind, and Takeda. The other authors report no financial relationships with commercial interests.
